The present invention broadly relates to concrete finishing machines. More particularly this invention relates to trowel blade adjustment mechanisms for motorized concrete finishing trowels. Art pertinent to the present invention is found in U.S. Class 404, Subclass 112.
Motorized finishing trowels are well known in the art. Typical trowels employ multiple, radially spaced apart blades that are secured to a motor-driven rotor. The rotor is forcibly revolved for finishing the concrete surface with the blades. The trowel blades rest directly on the concrete surface to be treated, so they support the machine's entire weight. Motorized trowels generally employ trowel blades that can be torsionally rotated relative to the concrete surface to change pitch. Both self-propelled "riding" trowels and manually "pushed" trowels (i.e., "walk-behind trowels") are well known in the art. Riding trowels have two or more blade-equipped rotors, whereas walk-behind trowels usually have single rotors.
Trowels may pass over the concrete surface several times as the concrete sets. The pitch of the blades is adjusted depending upon conditions. During the initial passes the blade pitch is relatively flat or horizontal. This spreads the weight of the machine over a relatively greater surface area, since the concrete is relatively wet and plastic at this time. During subsequent passes the concrete becomes less plastic, as it cures. The blade pitch is incrementally increased so the angle of incidence between the concrete surface and each blade face increases. During final passes the pitch of the blade may be near thirty degrees. Thus the blade pitch must be adjustable.
Manually manipulated motorized trowels are often referred to "power trowels" or "walk behind" trowels. Power trowels are generally comprised of a frame mounting a one cylinder internal combustion engine. Three or four horizontally-oriented, symmetrically disposed trowel blades are driven by the engine. Handlebar grips are generally provided on a handle extending from the frame to control the movement of the trowel during finishing operations.
Riding trowels are disclosed in U.S. Pat. Nos. 4,046,484 and 3,936,212 issued to Holz. Generally speaking riding trowels are comprised of a frame from which two or more rotating rotors downwardly project. A seat, mounted to the frame, is provided for the operator. The trowel is propelled by a self contained motor mounted on the frame. The weight of the trowel and the operator is transmitted frictionally to the concrete by the revolving blades. Locomotion results from the frictional forces between the blades and the surface. The rotors may be tilted from above to provide frictional differences that vector translate into steering forces. As these vector forces resolve, the desired trowel travel path is established. A yoke controlled bearing assembly is often employed to vary rotor pitch.
The pitch of the trowel blades may be manipulated by a swash plate that pushes downwardly on projections extending from the sides of the trowel blades. Downward force on the swash plate or pressure plate overcomes the machine's weight to adjust the pitch of the blades, by rotating them about their longitudinal axis. Various blade pitch control mechanisms have been provided on trowels. Most allow adjustment of blade pitch before and during finishing operations. One such mechanism is a lever-actuated blade pitch control unit. A lever arm adjustment mechanism such as a swash plate is pivotally coupled to the trowel frame at a position close to the central axis of the trowel blades. Adjustments are made by manipulating a rather lengthy lever. The lever is usually locked in place by a gear tooth and dog arrangement. Another blade pitch adjustment mechanism employs a knob located between the handlebar grips of the trowel handle. Rotation of the knob turns a finely threaded adjustment mechanism coupled to the swash plate. As a result the blade pitch may be gradually increased or decreased.
U.S. Pat. No. 4,577,993 discloses a power trowel having a knob actuated blade pitch adjustment mechanism that can readily be modified to incorporate a lever-actuated blade pitch adjustment mechanism.
Whiteman, U.S. Pat. No. 4,637,311 discloses a concrete finishing machine having a counter balanced blade pitch adjustment apparatus. A lever is interconnected to the blades with a spring-loaded cable. The spring assists in maintaining the adjustment handle and the blades at the desired setting.
U.S. Pat. No. 4,577,993 issued on Mar. 25, 1986 to J. Dewayne Allen, a coinventor herein. It discloses a power trowel with a cam-actuated blade pitch adjustment mechanism. This invention is a lever type mechanism employing a cam assembly to allow fine adjustment of the pitch of the blades of a trowel. Other patent issued to Allen include U.S. Pat. No. 5,108,220 and U.S. Pat. No. Des. 323,510 both of which relate to riding trowels.
U.S. Pat. No. 4,320,986 relates to rotary trowels. Tertinek, U.S. Pat. No. 4,232,980, discloses a rotary powered trowel and a knob adjustment for blade pitch. Carlstrom, U.S. Pat. No. 4,198,178 speaks of a concrete floor finisher that also employs a screw type adjustment for the pitch of the blades.
Whiteman, U.S. Pat. No. 4,312,603 discloses a twin trowel finishing machine that employs two counter rotating blades to enable a larger machine to be handled by a single person. This patent also discloses a screw adjustment for blade pitch control.
Regardless of the type of adjustment mechanism employed, the skilled trowel operator must normally make numerous repetitive pitch adjustments. Sometimes, for example, a job will be partially shaded, so pitch changes are necessary every time the operator moves between sunlight and shade. Thus, as will be appreciated by those skilled in the trowel arts, a straight forward, easy-to-use adjustment for controlling blade pitch is desirous. With either walk-behind or riding trowels, frequent adjustments to pitch can be time consuming and exhausting. It is generally desirable to minimize the time the operator must expend to make blade pitch adjustments.
Known prior art trowels usually include some type of secondary restraining mechanism that must be separately released before an adjustment of blade pitch is possible. Therefore, an ideal pitch adjustment needs to be convenient to use with minimal effort. Furthermore, for purposes of efficiency and safety, the device must lock automatically when released. Concurrently, it must unlock quickly when intentionally activated. When deployed, it must quickly and reliably establish a selected blade pitch that will be proportional to operator displacement. The pitch must be reliably maintained when the device is released.